The major drawback of existing key operated locks is that they are susceptible to being opened or picked by unauthorized persons. A person desiring to pick a lock can simply insert a foreign object or tool into the keyhole and thereby determine the location of the locking pins or tumblers by feeling with the foreign object until an area of resistance is encountered. This area of resistance indicates the position of the tumbler and once that position has been determined, the locking pin or tumbler can be moved to an unlocking position. As each tumbler is uncovered, it can be moved to an unlocking position and held their until all the locking tumblers or pins have been released. Look more specifically at a locking arrangement, such as that found on most doors which includes a rotatable doorknob for moving a bolt or latch from a locking position to an unlocking position, it should be noted that the doorknob is secured against rotation through direct contact with the tumblers. Therefore, force can be applied directly on the tumblers. Therefore, force can be applied directly on the tumblers which resist rotation of the doorknob. This resistance provides a means of feeling the arrangement of locking tumblers and accounts for the fact that existing locks are susceptible to picking. As each tumbler is released, it is wedged in its release position by rotation of the doorknob until all the tumblers have been released.
Furthermore, in considering existing lock structures it is generally the case that when a new locking arrangement is required, it is easier to replace the lock than to relocate the tumblers within the lock because the tumblers are usually permanently fixed therein.
The present invention provides a lock and coded key for operating that lock. The lock comprises a housing having a keyhole, a rotatable actuating member, a locking mechanism provided with a lockable portion moveable from a locking position to an unlocking position, first locking means, second locking means, a pusher member for pushing the key into contact with the first locking means, and a locking member. The lockable portion is normally held in its locking position by the first locking means. The second locking means is normally in a release position but is arranged so as to lock the lockable portion in its locking position when a key bearing an incorrect code is inserted in the lock. The tumblers prevent movement of the locking member through the actuating member by means of the lockable portion making it essentially impossible to pick the tumblers because they cannot be felt by moving the actuating member.
The key itself is coded to move the first locking means to a release position without disturbing the second locking means. The lockable portion is tensioned to move to its unlocking position when both the first and second locking means are in a release position. The actuating member is adapted to both operate the locking member when the lockable portion is in its locking position and to return the lockable portion to its locking position.